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Efficiencies of Some Spherical Ion Chambers in Continuous and Pulsed Radiation: A Numerical Evaluation.

Maghraby AM - Pol J Radiol (2015)

Bottom Line: Evaluation of the collection efficiencies of ion chambers is a necessity for the proper evaluation of radiation quantities in different applications.Through current work there is an attempt of focusing on how the selection of ion chamber dimensions may affect the overall collection efficiency in addition to the proper selection of other influencing parameters.Also, collection efficiencies considering diffusion current values (fd) were evaluated for the five chambers, and plotted versus the applied polarizing potential.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Faculty of Science - Alzulfi - Almajmaah University, Almajmaah, Saudi Arabia ; Department of Radiation Dosimetry, National Institute of Standards (NIS), Ionizing Radiation Metrology Laboratory, Giza, Egypt.

ABSTRACT

Background: Evaluation of the collection efficiencies of ion chambers is a necessity for the proper evaluation of radiation quantities in different applications. Overall collection efficiency is the product of three different values: collection efficiencies considering contributions of, volume recombination, back-diffusion loss and initial recombination, the later may be neglected at low charge rates.

Material/methods: Five common spherical ion chambers of different volumes and specifications were included in this study for the evaluation of volume recombination collection efficiency and back diffusion collection efficiency for continuous and pulsed radiation and at different values of the applied polarizing potential. Through current work there is an attempt of focusing on how the selection of ion chamber dimensions may affect the overall collection efficiency in addition to the proper selection of other influencing parameters.

Results: Collection efficiencies considering volume recombination (fv) for five spherical ion chambers of common types were evaluated for continuous and pulsed radiation over a wide range of polarizing potential. The relation between the ion chamber volume and its evaluated collection efficiencies were studied for both continuous and pulsed radiation; transit time values for the ion chambers included in this study were evaluated at different values of applied potential. Also, collection efficiencies considering diffusion current values (fd) were evaluated for the five chambers, and plotted versus the applied polarizing potential.

Conclusions: Through this study it was feasible to evaluate numerically the collection efficiencies of some spherical ion chambers considering volume recombination and back diffusion effects; the affecting parameters were studied and highlighted.

No MeSH data available.


Volume collection efficiency for continuous radiation (fV) values corresponding to different values of chamber volume (cm3) evaluated at different charge rate values (q̇).
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Related In: Results  -  Collection


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f2-poljradiol-80-515: Volume collection efficiency for continuous radiation (fV) values corresponding to different values of chamber volume (cm3) evaluated at different charge rate values (q̇).

Mentions: Because of the difference in volume and other dimensional characteristics between A3 (3.6 cm3) and A4 (30 cm3) it is noticeable that collection efficiency (fv) of A4 is lower, for example, at charge rate q̇=9.07×10−5 cm−3s−1, and using a polarizing potential of 700 V, fv for the A3 chamber was 0.9993 while for the A4 chamber it was 0.9877 which means that fv decreased by a factor of 1.15%, similarly for the A5 chamber (100 cm3), at the conditions, fv was 0.9449 i.e. less than for A3 by a factor of 5.4% and less than for A4 by a factor of 4.3%. At a much lower charge rate value (q̇=9.07×10−7 cm−3s−1), A6 (800 cm3) had volume collection efficiency of (fv)=0.9989 using polarizing potential of 700 V, while 0.8678 for the A8 ion chamber (15700 cm3). i.e. lower than for A6 by a factor of 13.12%. Figure 2 represents the relation between the volume collection efficiency as a function in the volume of the ion chamber evaluated at different charge rate values (q̇) evaluated at polarizing potential of V=700 V. This Figure does not represent a uniform behavior. This is because the chamber volume is not the influencing factor in defining fv (it is the effective electrode spacing [d]), and however, the general trend in Figure 2 clarifies the decrease of fv as the chamber volume increases, this may be due to the special geometrical or technical requirements for the design of large-volume ion chambers. Similar figures like Figure 2 can be plotted for other V values.


Efficiencies of Some Spherical Ion Chambers in Continuous and Pulsed Radiation: A Numerical Evaluation.

Maghraby AM - Pol J Radiol (2015)

Volume collection efficiency for continuous radiation (fV) values corresponding to different values of chamber volume (cm3) evaluated at different charge rate values (q̇).
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4664224&req=5

f2-poljradiol-80-515: Volume collection efficiency for continuous radiation (fV) values corresponding to different values of chamber volume (cm3) evaluated at different charge rate values (q̇).
Mentions: Because of the difference in volume and other dimensional characteristics between A3 (3.6 cm3) and A4 (30 cm3) it is noticeable that collection efficiency (fv) of A4 is lower, for example, at charge rate q̇=9.07×10−5 cm−3s−1, and using a polarizing potential of 700 V, fv for the A3 chamber was 0.9993 while for the A4 chamber it was 0.9877 which means that fv decreased by a factor of 1.15%, similarly for the A5 chamber (100 cm3), at the conditions, fv was 0.9449 i.e. less than for A3 by a factor of 5.4% and less than for A4 by a factor of 4.3%. At a much lower charge rate value (q̇=9.07×10−7 cm−3s−1), A6 (800 cm3) had volume collection efficiency of (fv)=0.9989 using polarizing potential of 700 V, while 0.8678 for the A8 ion chamber (15700 cm3). i.e. lower than for A6 by a factor of 13.12%. Figure 2 represents the relation between the volume collection efficiency as a function in the volume of the ion chamber evaluated at different charge rate values (q̇) evaluated at polarizing potential of V=700 V. This Figure does not represent a uniform behavior. This is because the chamber volume is not the influencing factor in defining fv (it is the effective electrode spacing [d]), and however, the general trend in Figure 2 clarifies the decrease of fv as the chamber volume increases, this may be due to the special geometrical or technical requirements for the design of large-volume ion chambers. Similar figures like Figure 2 can be plotted for other V values.

Bottom Line: Evaluation of the collection efficiencies of ion chambers is a necessity for the proper evaluation of radiation quantities in different applications.Through current work there is an attempt of focusing on how the selection of ion chamber dimensions may affect the overall collection efficiency in addition to the proper selection of other influencing parameters.Also, collection efficiencies considering diffusion current values (fd) were evaluated for the five chambers, and plotted versus the applied polarizing potential.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Faculty of Science - Alzulfi - Almajmaah University, Almajmaah, Saudi Arabia ; Department of Radiation Dosimetry, National Institute of Standards (NIS), Ionizing Radiation Metrology Laboratory, Giza, Egypt.

ABSTRACT

Background: Evaluation of the collection efficiencies of ion chambers is a necessity for the proper evaluation of radiation quantities in different applications. Overall collection efficiency is the product of three different values: collection efficiencies considering contributions of, volume recombination, back-diffusion loss and initial recombination, the later may be neglected at low charge rates.

Material/methods: Five common spherical ion chambers of different volumes and specifications were included in this study for the evaluation of volume recombination collection efficiency and back diffusion collection efficiency for continuous and pulsed radiation and at different values of the applied polarizing potential. Through current work there is an attempt of focusing on how the selection of ion chamber dimensions may affect the overall collection efficiency in addition to the proper selection of other influencing parameters.

Results: Collection efficiencies considering volume recombination (fv) for five spherical ion chambers of common types were evaluated for continuous and pulsed radiation over a wide range of polarizing potential. The relation between the ion chamber volume and its evaluated collection efficiencies were studied for both continuous and pulsed radiation; transit time values for the ion chambers included in this study were evaluated at different values of applied potential. Also, collection efficiencies considering diffusion current values (fd) were evaluated for the five chambers, and plotted versus the applied polarizing potential.

Conclusions: Through this study it was feasible to evaluate numerically the collection efficiencies of some spherical ion chambers considering volume recombination and back diffusion effects; the affecting parameters were studied and highlighted.

No MeSH data available.